Browsing by Author "Cram, SL"

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    Crystallization of TiO2 powders and thin films prepared from modified titanium alkoxide precursors
    (Wiley-Blackwell, 2008-06) Karatchevtseva, I; Cassidy, DJ; Zhang, Z; Triani, G; Finnie, KS; Cram, SL; Barbé, CJ
    The modification of titanium alkoxides by chemical reactions with ligands yields complexes or molecular clusters that are substantially different from those of the parent alkoxides. In this study, we investigate the structural evolution of powders and thin films prepared from two titanium oxo-alkoxyacylate clusters with different oxo-core structures [Ti6(μ3-O)2(μ2-O)2](CH3COO)8(μ2-OiPr)2(OiPr)6 and [Ti6(μ3-O)6](μ-RCOO)6(OiPr)6 ([6,4] and [6,6], respectively) as a function of annealing temperature. The structural evolution of powders and thin films prepared from the corresponding parent alkoxide Ti(OiPr)4 (TiP) were also investigated for comparison. In all powders, the amorphous-to-anatase transformation occurred upon heating to 400°C. In sharp contrast, the anatase-to-rutile transformation of the powder prepared from the [6,6] cluster was significantly inhibited compared with the conventionally derived powder, with no rutile being detected even after annealing at 800°C for 1 h. This was attributed to the small crystallite size in the [6,6]-derived powder, which is lower than the critical size previously reported for the anatase-to-rutile transformation in similar sol–gel-derived materials. In thin films, the amorphous-to-anatase phase transition also occurred at temperatures as low as 400°C for coatings deposited from conventional TiP precursor and [6,4] cluster solutions. However, in contrast to the corresponding powders no rutile nucleation occurred even at 800°C in either film. © 2008, Wiley-Blackwell.
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    A SANS study of the adsorption of guar gum on talc surfaces
    (Australian Nuclear Science and Technology Organisation, 2001-10) Cram, SL; Knott, RB; Hanley, HJM
    Reagents based on guar gum are commonly used as 'gangue' depressants in the flotation of sulphides from ores containing naturally floating layer silicate minerals such as talc. Nickel sulphide ores processed by WMC Resources Ltd. at the Leinster Nickel Operations in Western Australia typically contain 1-2 % talc. Guar gum added to the flotation cell depresses the talc by adsorbing onto its surface thereby reducing its hydrophobic nature. Guar gum is a long chain polysaccharide containing many hydroxyl functional groups along the length of its chain. The ratio of chain length to the number of hydroxyl and carboxyl groups causes the guar gum to be selective in depressing talc rather than nickel sulphide minerals. Small angle neutron scattering (SANS) it is an excellent tool for probing structures in the nano length scale. Unlike X-rays neutrons are sensitive to low atomic weight elements especially hydrogen and therefore organics. Using SANS it is possible to contrast different parts of a composite sample to get information on spatial arrangements. These qualities make SANS an obvious choice for studying the adsorption of guar gum on the surface of talc in aqueous solutions. Complimentary SANS experiments were carried out in Australia at the Australian Nuclear Science and Technology Organisation (ANSTO) and in the United States at the National Institute of Standards and Technology (NIST). Initially talc samples were studied 'as supplied' however as experiments proceeded attempts to reduce the particle size and distribution were carried out by milling and centrifuging procedures. Contrast matching techniques were used to observed the scattering behaviour of talc with and without the presence of guar gum and vice versa over a total q range of 0.002 - 0.1 Angstroms - 1. The size of the talc particles appears to affect the scattering behaviour not only of talc but also of guar gum in the same solutions. This implies that the structure of the guar gum is strongly influenced by the dimensions of the talc and could be taken as indirect evidence of adsorption of guar gum onto the talc surface. Although adsorption has been implied a model of the adsorption mechanism cannot be proposed from these preliminary results. In order to achieve this more homogeneous talc samples need to be studied; in particular the poly dispersity of and impurities in the samples must be addressed.